1. Field of the Invention
The present invention generally relates to a railway or railroad track joint, and more particularly, to an improved electrically insulated bonded rail joint incorporating a non-conductive spacer in or associated with a rail bonding adhesive. The present invention also relates to a method for bonding such electrically insulated rail joints. The present invention provides more control over the spacing of the adhesive layer to achieve a stronger joint and a more predictable and stable electrical insulation of a track circuit with improved bonding.
2. Description of the Prior Art
Joining of two railroad rails has had quite a varied history. Originally, two rail ends were butted together, and "bars" or "fishplates" generally about three feet long, were used as scabs across the rail joint, one inside and one outside of the rail. The "bars" or "fishplates" and the rails were drilled to accept bolts, which once inserted and tightened, held the rails and fishplates together as one piece.
One limitation associated with joining two rails in this manner is that there is metal-to-metal contact between the rails and the fishplates, which results in rail joints that are not electrically insulated from each other. Electrical insulation between adjoining rails is desired in some applications within the rail industry. For example, where rails are electrically insulated from their adjoining rails, the metal wheels or trucks of a train or similar railed vehicle crossing the insulated rails can be used to complete an electrical circuit. The completed electrical circuit is used in many applications, such as triggering signalling devices further down the track, moving switches, or sending computer signals to locate the train on the track for a central dispatcher.
The first attempts to electrically insulate rail joints simply consisted of a flexible, formed, durable insulating material inserted between the fishplates and the rails, and between the butted rail ends. However, this is far from the present state of the art.
The second stage in the evolution of the development of electrically insulated rail joints, provided for embedding the metal fishplates within an insulating shielding material. Most commonly polyurethane is chosen as the insulating material for this application.
The third stage in the evolution of the development or the rail joints was the formation of "bonded" railroad rail joints. With bonded railroad rail joints, a rail bonding adhesive, typically an epoxy material, is used to chemically glue or bond the fishplates and rails together as one unit. Additionally, in some applications, a web-like or matting material is inserted between the fishplates and the rails which is coated on one or both sides with rail bonding adhesive. The bonded rail joint is typically the strongest rail joint and is a very solid rail joining means. Bonded rail joints prevent movement of one bonded rail relative to the other bonded rail. While bolts similar to those described above are still used in this application, the bolts function mainly as a press to hold the rail bonding adhesive, the fishplates and the rails together until the adhesive sets and forms the bond.
With the bonded railroad rail joints discussed above, to form an electrically insulated as well as a bonded rail joint, two rail ends are butted with an insulating material inserted therebetween. The insulating material between the rail ends is often called an "end post". Further, the vertical surfaces of the rails are coated on the inside and outside with a layer of rail bonding adhesive for a distance of about 1.5 feet on both sides of the point where the rail ends abut the insulating material. "Inside" and "outside" means here with respect to the track itself as though the rail was installed on a track bed, with "inside" denoting the rail surface between the rails and "outside" denoting the surface of the rail opposite the "inside" surface. In some applications, a layer of matting material, which is typically made of fiberglass and is on the order of 1/16 inch thick and is quite shapable, is laid on top of the rail bonding adhesive layer. The matting material layer is in turn covered with another layer of rail bonding adhesive. The rail bonding adhesive soaks through the matting layer. Subsequently, metal fishplates are placed on the inside and outside of the rails and bolts (usually 4-6) are installed horizontally (with respect to the track bed) through the two fishplates and the rails. The tightening of the bolts holds the fishplates, rail bonding adhesive and rails together as one unit while the rail bonding adhesive sets. The rail bonding adhesive can cure at ambient temperatures or at elevated temperatures. The resulting rail joint bond is quite strong and electrically insulated.
A limitation of the bonded/insulated rail joint is that the process of tightening the nuts on the bolts squeezes out all or nearly all of the rail bonding adhesive and crushes the matting material layer, resulting in a very thin adhesive layer in the rail bonding joint. This results in a weaker bonded rail joint and less electrical insulating capability.
Attempts have been made in the prior art to provide a spacer between the fishplates and the rails to prevent the formation of an unacceptably thin adhesive layer in the rail bonding joint. U.S. Pat. No. 3,381,892 to Eisses discloses a rail joint construction which includes an insulating layer comprising a cold hardening paste layer 6 which is surrounded by nylon rods 9 and 10. The nylon rods 9 and 10 serve as spacing elements spacing the fishplates 3 and 4 from the rails 1 and 2.
British Patent No. 2,071,187 discloses an insulated rail joint comprising a fishplate of insulating material having a series of vertical ribs spaced along its rail engaging faces. The plastic material of the fishplate may include abrasive-proof grains suspended within the plastic. The abrasive-proof grains are apparently intended to increase the frictional engagement of the ribs with the rail and do not perform a spacing function.
However, none of the prior art references discloses a bonded rail joint or method of making a bonded rail joint wherein the thickness of the rail bonding adhesive layer and the corresponding degree of electrical insulation can be easily modified at will to provide a bonded rail joint of a desired thickness and electrical insulating capability. Thus, a need exits in the prior art for a bonded rail joint and for a method of making a bonded rail joint wherein the thickness of the adhesive layer in the bonded rail joint can be easily and reliably modified at will to provide a rail joint having an adhesive layer of a desired thickness and insulating capability whether manufactured under factory or field conditions.